The present invention relates to a displacement measurement apparatus which detects displacement distribution in the direction of a height of a convex portion or a concave portion formed on the surface of a card.
There is available a detection apparatus of an optical system for displacement on the surface having the structure shown in FIG. 23, as an apparatus for detecting displacement distribution in the direction of a height formed on the surface of an object to be inspected.
In the drawing, the numeral 1 represents a linear light source which emits linear light.
As shown in FIG. 24, the linear light source 1 is composed of light source 3 and cylindrical cover 7 which contains the light source 3 and has on its end surface slit 5 representing a linear light generating means.
In FIG. 23 again, a linear light emitted from the linear light source 1 is projected on object to be inspected 11 through rotary mirror 9 serving as a scanning means.
Reflected light from the object to be inspected 11 enters PSD (semiconductor position detection element) array 13 divided into plural pieces in the linear direction of the linear light, and thereby, displacement distribution on the surface of the object to be inspected 11 is detected.
In recent years, there has spread a card 21 having an arrangement shown in FIG. 25.
The numeral 23 represents a magnetic stripe on which magnetic information is recorded, and 25 represents a character row formed by a convex portion or a concave portion (12345678910, Konica Tarou, in FIG. 25).
When reading a convex portion or a concave portion (displacement in the direction of a height on the surface) on card 21 by the use of the detection apparatus of an optical system for displacement on the surface, if the card 21 has been subjected to printing and reflectance for light on the surface of the card 21 has been lowered accordingly, the convex portion or the concave portion can not be read accurately, which is a problem.
The invention has been achieved in view of the problem mentioned above, and its object is to provide a displacement measurement apparatus wherein a convex portion or a concave portion on a card can be read accurately even in the case of a card having poor reflectance.
The above object can be attained by the following structures.
Structure (1-1) A surface displacement detecting apparatus for detecting a concave, a convex or a hole on a surface of a detection object, comprises:
a light shielding device provided in a direction crossing the surface of the detection object,
a light irradiating device provided at one side of the light shielding device and to irradiate the detection object with light;
a light receiving device provided at the other side of the light shielding device and to receive at least one of regular reflection light and diffuse reflection light from the surface of the detection object; and
a conveyor to convey at least one of the detection object and the light irradiating device.
Structure (1-2) In the surface displacement detecting apparatus of (1-1), the light irradiating device comprises a light source and an optical element to irradiate the detection object with the light emitted from the light source and the light receiving device comprises a condenser lens to condense at least one of the regular reflection light and the diffuse reflection light from the surface of the detection object and a light receiving element to receive the condensed light.
Structure (1-3) In the surface displacement detecting apparatus of (1-2), the light irradiating device shapes the light in a line and irradiates the detection object with the line-shaped light.
Structure (1-4) In the surface displacement detecting apparatus of (1-2), the optical element is a cylindrical lens.
Structure (1-5) In the surface displacement detecting apparatus of (1-2), the light irradiating device forms a plurality of spot light aligned in a straight line as the light and irradiates the detection object with the plurality of spot light.
Structure (1-6) In the surface displacement detecting apparatus of (1-5), wherein the optical element is a micro lens array.
Structure (1-7) In the surface displacement detecting apparatus of (1-1), wherein the detection object comprises a flat surface and a concave and the light irradiating device, the light shielding device and the light receiving device are arranged such that light reflected from the flat surface is shielded by the light shielding device and light reflected from the concave proceeds to the light receiving element.
Structure (1-8) In the surface displacement detecting apparatus of (1-1), the detection object comprises a flat surface and a concave and the light irradiating device, the light shielding device and the light receiving device are arranged such that light diffused from the flat surface is shielded by the light shielding device and light diffused from the concave proceeds to the light receiving element.
Structure (1-9) In the surface displacement detecting apparatus of (1-1), the width of the light on the detection object is smaller than the width of the concave, the convex or the hole.
Structure (1-10) In the surface displacement detecting apparatus of (1-2), the surface displacement detecting apparatus detects the concave, the convex or the hole from a light receiving position on the light receiving element.
Structure (1-11) In the surface displacement detecting apparatus of (1-2), the light receiving device comprises a plurality of light receiving elements aligned in a straight line as the light receiving element or the light receiving element is split into a plurality of light receiving elements aligned in a straight line.
Structure (1-12) In the surface displacement detecting apparatus of (1-2), the light receiving elements are a PSD array in which n pieces of PSD are arranged in a predetermined direction or PD which is split into n pieces in a predetermined direction and into m pieces in a direction perpendicular to the predetermined direction, where n is an integer not less than 2 and m is an integer not less than 1.
Structure (1-13) In the surface displacement detecting apparatus of (1-3), the light receiving elements are a PSD array in which n pieces of PSD are arranged in a direction along the line-shaped light or PD which is split into n pieces in a direction along the line-shaped light and m pieces in a direction perpendicular to along the line-shaped light, where n is an integer not less than 2 and into m is an integer not less than 1.
Structure (1-14) In the surface displacement detecting apparatus of (1-5), the light receiving elements are a PSD array in which n pieces of PSD are arranged in a direction along the plurality of aligned spot light or PD which is split into n pieces in a direction along the plurality of aligned spot light and into m pieces in a direction perpendicular to along the plurality of aligned spot light, where n is an integer not less than 2 and m is an integer not less than 1.
Structure (1-15) In the surface displacement detecting apparatus of (1-1), the light shielding device is shiftable in a direction crossing the surface of the detection object and the light shielding device is brought in contact with the detection object.
Structure (1-16) In the surface displacement detecting apparatus of (1-1), the light shielding device has an edge surface facing the detection object and is arranged to form a space between the edge surface and the detection object.
Structure (1-17) In the surface displacement detecting apparatus of (1-10), the light receiving position on the light receiving element displaces in a direction parallel to the light receiving element.
Structure (1-18) In the surface displacement detecting apparatus of (1-1), the detection object is a card having the concave, the convex or the hole.
Structure (1-19) In the surface displacement detecting apparatus of (1-1), a range of the displacement of the concave, the convex or the hole on the detection object is not larger than 1.0 mm.
Structure (1-20) In the surface displacement detecting apparatus of claim 1, the surface displacement detecting apparatus detects an amount of the displacement of the concave, the convex or the hole.
Structure (1-21) An optical pickup apparatus for use in a surface displacement detecting apparatus for detecting a concave, a convex or a hole on a surface of a detection object, comprises:
a light shielding device provided in a direction crossing the surface of the detection object,
a light irradiating device provided at one side of the light shielding device and to irradiate the detection object with light; and
a light receiving device provided at the other side of the light shielding device and to receive at least one of regular reflection light and diffuse reflection light from the surface of the detection object.
There will be explained another embodiment wherein discrimination between a flat portion and a concave portion, or a convex portion, or a hole portion is easy even in the case of a card having poor reflectance for light. Incidentally, it is possible to combine the following structures with the invention at any time, or to combine the following embodiments themselves.
Structure (2-1)
A surface displacement detection apparatus comprising plural contact type displacement detection sensors, wherein aforesaid plural contact type displacement detection sensors are arranged to be in a two-dimensional form, and the plural contact type displacement detection sensors are in contact with an object to be inspected so that a concave portion, a convex portion or a hole portion of the object to be inspected is detected.
Structure (2-2)
The surface displacement detection apparatus according to Structure (2-1), wherein the object to be inspected stated above is a card having a concave portion, a convex portion or a hole portion.
Structure (2-3)
The surface displacement detection apparatus according to Structure (2-1), wherein a range of displacement of a concave portion, a convex portion or a hole portion of the object to be inspected stated above is not more than 1.0 mm.
Structure (2-4)
The surface displacement detection apparatus according to Structure (2-1), wherein an amount of displacement of a concave portion, a convex portion or a hole portion of the object to be inspected is detected by the aforesaid surface displacement detection apparatus.
Structure (2-5)
The surface displacement detection apparatus according to Structure (2-1), wherein a width of one of the aforesaid contact type displacement detection sensors is smaller than that of a concave portion, a convex portion or a hole portion of the object to be inspected.
Structure (2-6)
The surface displacement detection apparatus according to Structure (2-1) having therein a pattern recognition section which recognizes patterns on the surface of the object to be inspected from information of a concave portion, a convex portion or a hole portion of the object to be inspected.
Structure (2-7)
The surface displacement detection apparatus according to Structure (2-1), wherein the contact type displacement detection sensor recognizes a concave portion, a convex portion or a hole portion of the object to be inspected by the fluctuation of a value of resistance.
Structure (2-8)
The surface displacement detection apparatus according to Structure (2-1), wherein the contact type displacement detection sensor recognizes a concave portion, a convex portion or a hole portion of the object to be inspected by the fluctuation of a value of electrostatic capacity.
Structure (2-9)
The surface displacement detection apparatus according to Structure (2-1), wherein the contact type displacement detection sensor is a linear encoder.
Structure (2-10)
A method of detecting a concave portion, a convex portion or a hole portion of the object to be inspected comprising a step to bring an object to be inspected into contact with the surface displacement detection apparatus and a step to detect a concave portion, a convex portion or a hole portion of the object to be inspected, wherein a surface displacement detection apparatus has plural contact type displacement detection sensors which are arranged to be in the two-dimensional form, and the plural contact type displacement detection sensors come in contact with an object to be inspected to detect a concave portion, a convex portion or a hole portion of the object to be inspected.
The invention described in Structure (3-1) to solve the problems stated above is represented by a displacement measurement apparatus composed of a light-shielding means which is provided in the direction to cross the surface of the card above that card on which the characters are formed by convex portions or concave portions, a light irradiating means which is provided on one side of the light-shielding means and projects linear light on the card, a light-receiving means which is provided on the other side of the light-shielding means and receives at least one of a regular reflected light on the surface of the card and a diffused light, and of a conveyance means which conveys at least one of the card and the light irradiating means in the direction to cross the direction of a line of the linear light.
When a leading edge portion of the light-shielding means is provided to be located in the vicinity of the surface (flat portion) of the card under the condition that a character is formed by a concave portion, regular reflected light and diffused light on the flat section are cut by the light-shielding means more, compared with regular reflected light and diffused light on the concave portion, thus, a central position and an angle of an effective incident light are changed when the incident light enter the light-receiving means.
Accordingly, discrimination between the flat portion and the concave portion is easy even in the case of a card having poor reflectance for light.
Further, when a leading edge portion of the light-shielding means is provided to be located in the vicinity of the convex portion of the card under the condition that a character is formed by a convex portion, regular reflected light and diffused light on the convex portion are cut by the light-shielding means more, compared with regular reflected light and diffused light on the flat portion, thus, a central position and an angle of an effective incident light are changed when the incident light enter the light-receiving means.
Accordingly, discrimination between the flat portion and the concave portion is easy even in the case of a card having poor reflectance for light.
The invention described in Structure (3-2) is a displacement measurement apparatus wherein the light irradiating means described in Structure (3-1) has a cylindrical lens and irradiates a linear light on the card mentioned above.
By using a cylindrical lens, it is possible to achieve cost reduction.
The invention described in Structure (3-3) is a displacement measurement apparatus wherein the light irradiating means of the invention described in Structure (3-1) has a micro-lens array, and plural spotlight beams arranged mostly on a straight line are irradiated on the aforesaid card.
When intensity of a light source is distributed sharply, intensity of an individual spotlight can be adjusted individually by a lens area, so that uniform spotlight can be irradiated.
Further, by using a micro-lens array, it is also possible to employ a beam size method wherein judgment is made by a diameter of a beam arriving at a light-receiving means, when discriminating a flat portion, a convex portion or a convex portion of a card.
The invention described in Structure (3-4) is a displacement measurement apparatus wherein a card of the invention described in either one of Structure (3-1)-Structure (3-3) is composed of a flat portion and a concave portion, and the light irradiating means and the light-shielding means are arranged so that a reflected light from the flat portion is interrupted by the light-shielding means and a reflected light from the concave portion advances to the light-receiving means.
By arranging the light irradiating means and the light-shielding means so that the regular reflected light reflected on the flat portion is interrupted by the light-shielding means and a regular reflected light reflected on the concave portion advances to the light-receiving means, discrimination between the flat portion and the concave portion is easy because it is possible to select a concave portion if a regular reflected light comes, and to select a flat portion if a regular reflected light does not come.
The invention described in Structure (3-5) is a displacement measurement apparatus wherein the card of the invention described in either one of Structure (3-1)-Structure (3-3) is composed of a flat portion and a concave portion, and the light irradiating means and the light-shielding means are arranged so that a diffused light from the flat portion is interrupted by the light-shielding means and only a diffused light from the concave portion advances to the light-receiving means.
By arranging the light irradiating means and the light-shielding means so that a diffused light from the flat portion is interrupted by the light-shielding means and only a diffused-light from the concave portion advances to the light-receiving means, discrimination between the flat portion and the concave portion is easy because it is possible to select a concave portion if a diffused light comes, and to select a flat portion if a diffused light does not come.
Unlike the regular reflected light, the diffused light is uniformly diverged at a certain solid angle.
Therefore, a degree of freedom of a position of the light-receiving means is enhanced, which makes it possible to discriminate between a flat portion and a concave portion or between a flat portion and a convex portion.
The invention described in Structure (3-6) is a displacement measurement apparatus wherein a width of a linear light from the light irradiating means described in either one of Structure (3-1)-Structure (3-3) is smaller than a width of the convex portion or of the concave portion.
By making a width of a linear light from the light irradiating means to be smaller than a width (preferably, the smallest width) of the convex portion or of the concave portion, it is possible to generate the condition wherein the linear light is projected on the convex portion or the concave portion, and is not projected on the flat portion.
It is therefore easy to detect a convex portion, a concave portion or a flat portion, reading accuracy for a concave portion or a convex portion is improved.
The invention described in Structure (3-7) is a displacement measurement apparatus wherein the light-receiving means of the invention described in either one of Structure (3-1)-structure (3-6) is either one of PD divided into the number n (n represents integers of 2 or more) in the linear direction of the linear light and divided into the number m (m represents integers of 1 or more) in the direction crossing the linear direction and PSD array arranged in quantity of n (n represents integers of 2 or more) in the linear direction of the linear light.
By using either one of PD divided into the number n (n represents integers of 2 or more) in the linear direction of the linear light and divided into the number m (m represents integers of 1 or more) in the direction crossing the linear direction and PSD array arranged in quantity of n in the linear direction of the linear light, it is possible to obtain information not only of intensity of light to be received but also of the central position of brightness of light to be received, and thereby, reading accuracy for a flat portion, a concave portion or a convex portion is improved.
The invention described in Structure (3-8) is a displacement measurement apparatus wherein the light-shielding means of the invention described in either one of Structure (3-1)-Structure (3-7) is provided to be movable in the direction almost crossing the surface of the card and is brought into contact with the surface of the card.
Since the light-shielding means is provided to be movable in the direction almost crossing the surface of the card and is brought into contact with the surface of the card, the light-shielding means can move while tracing the surface of the card to conduct light-shielding even when the card is bent or even when a thin IC chip is provided on the surface of the card. Thus, reading accuracy for a flat portion and a concave portion or a flat portion and a convex portion is improved.
The invention described. in Structure (3-9) is a displacement measurement apparatus wherein the light-shielding means of the invention described in either one of Structure (3-1)-Structure (3-7) has a contact portion which is brought into contact with a portion other than the aforesaid card so that a clearance may be formed between an end surface facing the card and the surface of the card.
Since there is provided a contact portion which is brought into contact with a portion other than the aforesaid card so that a clearance may be formed between an end surface facing the card and the surface of the card, even when the card is bent or a thin IC chip is provided on the surface of the card, the light-shielding means does not interfere with the card, and reading of a flat portion and a concave portion or a flat portion and a convex portion can be conducted.
The invention described in Structure (3-10) is a displacement measurement apparatus having therein a light irradiating means which irradiates a linear light on a card having on its surface a character formed by a convex portion or a concave portion, a light-receiving means which receives at least one of a regular reflected light and a diffused light on the surface of the card, and a conveyance means which conveys at least one of the card and the light irradiating means in the direction crossing the linear direction of the linear light, wherein, the light-receiving means has PD array whose light-receiving surface is divided into two, and is provided so that light from a flat portion of the card may irradiate a light-receiving surface on one side of the two divided light-receiving surfaces and light from the convex portion of the concave portion may irradiate both of the two divided light-receiving surfaces.
If an arrangement is made so that light from a flat portion of the card may irradiate both light-receiving surfaces of the two divided light-receiving surfaces and light from a convex portion or a concave portion may irradiate a light-receiving surface on one side of the two divided light-receiving surfaces, in opposition to the case where light from a flat portion of the card may irradiate a light-receiving surface on one side of the two divided light-receiving surfaces and light from the convex portion of the concave portion may irradiate both of the two divided light-receiving surfaces, it is possible to obtain signals having no connection with light intensity by taking a value of (Axe2x88x92B)/(A+B) when two divided light-receiving surfaces are represented respectively by A and B, and it is possible to read a convex portion or a concave portion accurately even when the reflectance of light on the surface of the card is lowered.
When a circuit to operate division of (Axe2x88x92B)/(A+B) complicated and expensive, APC (automatic power control) is applied on a light source so that output of A or B may always be constant, and a value of (Axe2x88x92B) only is outputted. Due to this, it is possible to obtain the same results as in division on a pseudo basis.
Further, when division of the light-receiving surface is made to be asymmetric, higher sensitivity is obtained.
The invention described in Structure (3-11) is a displacement measurement apparatus having therein a light irradiating means which irradiates a linear light on a card having on its surface a character formed by a convex portion or a concave portion, a light-receiving means which receives at least one of a regular reflected light and a diffused light on the surface of the card, and a conveyance means which conveys at least one of the card and the light irradiating means in the direction crossing the linear direction of the linear light, wherein, the light-receiving means has PD array whose light-receiving surface is divided into three.
When there are formed two portions (for example, a black portion and a white portion) each having different reflectance on the card through printing, there is a fear that even a flat portion is misjudged to be a convex portion or a concave portion. However, when a value of ((A+C)xe2x88x92B)/(A+B+C) is taken under the assumption that output of three divided light-receiving surfaces are represented respectively by A, B and C, even when reflectance in the vicinity of a convex portion or a concave portion is fluctuated sharply, misjudgment is lessened because output corresponding to unevenness is performed without being influenced by sharp fluctuation of reflectance.
In place of operating division of ((A+C)xe2x88x92B)/(A+B+C), APC (automatic power control) is applied on a light source so that output of (A+C) or of B may always be constant. Then, a value of (A+C)xe2x88x92B only is outputted. Due to this, it is possible to obtain the same output results as in division on a pseudo basis. In particular, when (A+C) is made to be constant, fluctuation of reflectance caused by various patterns on the card tends not to be caused. On this point, an effect of the invention described in Structure 11 is much higher than that of the invention described in Structure 10.
Though a value of ((A+C)xe2x88x92B) only is outputted for sharp fluctuation of unevenness, only this makes output to be changed sharply by the change of unevenness, which makes it easy to compare a flat surface with unevenness.
The invention described in Structure (3-12) is a displacement measurement apparatus wherein the light irradiating means of the invention described in Structure (3-10) or in Structure (3-11) has therein a light source, a light-shielding plate which is provided in a parallel light flux emitted from the light source and made to be a parallel light flux, and splits the parallel light flux into two light fluxes, and a lens which condenses the aforesaid two light fluxes on the card.
If two light fluxes are made to coincide with each other on either a flat portion of the card or a concave portion or a convex portion on one side, two light fluxes exist on the remote portion on the other side.
Therefore, by using a light-receiving element whose light-receiving surface is split into two or three, it is possible to detect a convex portion or a concave portion.
When light is condensed on a flat portion, if PD whose light-receiving surface is split into three is used, light is condensed on the central light-receiving surface among three split light-receiving surfaces and misjudgment to cause no misjudgment, even when two portions (for example, a black portion and a white portion) each having different reflectance are formed on the card through printing.
Incidentally, as an optical system of this kind, a telecentric optical system wherein a distance of a reading optical system is proportional to a distance between two beams is more preferable.
The invention described in Structure (3-13) is a displacement measurement apparatus wherein the light irradiating means of the invention described in Structure (3-11) has therein two light sources each emitting a parallel light flux and two lenses each converging each of two light fluxes on the card.
If light converging is conducted on either a flat portion of the card or a concave portion or a convex portion on one side, two light fluxes exist on the portion on the other side.
Therefore, by using a light-receiving element whose light-receiving surface is split into two or three, it is possible to detect a convex portion or a concave portion.
When light is condensed on a flat portion, if PD whose light-receiving surface is split into three is used, light is condensed on the central light-receiving surface among three split light-receiving surfaces and misjudgment to cause no misjudgment, even when two portions (for example, a black portion and a white portion) each having different reflectance are formed on the card through printing.
When realizing a telecentric optical system by using one light source, its design is somewhat difficult. However, by providing each light source, it is possible to realize an inexpensive and accurate optical system which conducts telecentric behaviors.
The invention described in Structure (3-14) is a displacement measurement apparatus having therein a light irradiating means which irradiates linear light on a card having on its surface a character formed by a convex portion or a concave portion, a light-receiving means which receives at least one of regular reflected light and diffused light on the surface of the card and a conveyance means which conveys at least one of the card and the light irradiating means in the direction crossing the linear direction of the linear light, wherein the light irradiating means has a micro-lens array and irradiates, on the card, spotlight beams arranged almost in a straight line, and the light-receiving means has a micro-lens array corresponding to the spotlight beams and PD whose light-receiving surface is split into multiple concentric circles so that each of the concentric circles may correspond to each micro-lens array.
When a light flux coming out of each lens of the micro-lens array is detected through a beam size method by using PD whose light-receiving surface is split into two or more concentric circles, discrimination between a flat portion and a concave portion is easy even when a change in light to be received is great and reflectance of light on the card is poor.
The invention described in Structure (3-15) is a displacement measurement apparatus having therein a contact means having a contact type displacement detection sensor which is brought into contact with a card having on its surface a character formed by a convex portion or a concave portion, and a conveyance means which conveys at least one of the card and the contact means.
By detecting directly a flat portion and a convex portion or a concave portion of the card, discrimination between a flat portion and a concave portion is easy even in the case of a card having poor reflectance of light.
A contact type displacement detection sensor includes one wherein a resistance value is changed depending on the position of a contact like in the invention described in Structure (3-16), and one wherein an electrostatic capacity is changed depending on the position of a contact like in the invention described in Structure (3-17).
The invention described in Structure (3-18) is a displacement measurement apparatus having therein a contact means which is provided to be in contact with a card having on its surface a character formed by a convex portion or a concave portion, and in which plural contact type displacement detection sensors are arranged on a two-dimensional basis on at least a portion where the character is formed.
By detecting directly a flat portion and a convex portion or a concave portion of the card, discrimination between a flat portion and a concave portion or a convex portion is easy despite the card having poor reflectance of light.
Due to the contact means which is provided to be in contact with a card having on its surface a character formed by a convex portion or a concave portion, and in which plural contact type displacement detection sensors are arranged on a two-dimensional basis on at least a portion where the character is formed, detection can be conducted at a time, and a conveyance means which conveys at least one of the card and the contact means is made to be unnecessary.
The invention described in Structure (3-19) is a displacement measurement apparatus having therein a light irradiating means which irradiates light having directivity on a card having on its surface a character formed by a convex portion of a concave portion, a converging lens which condenses regular reflected light on a flat portion other than a convex portion and a concave portion on the card, and a light-receiving means which is provided at the position which is conjugate for the surface of the card through the converging lens, and at which the regular reflected light condensed by the converging lens enters.
Among light irradiated on the card, light reflected on the flat portion other than a convex portion or a concave portion is condensed by the converging lens and advances to the light-receiving means, while, light reflected on a convex portion or a concave portion advances to a destination other than the light-receiving means, especially in the case of a curved surface which is different from a flat surface of a flat portion, such as the case where the sectional form on the surface is almost a circular arc like a convex portion or a concave portion formed through embossing.
Accordingly, the portion where the light-receiving means does not receive light, or the portion where the light-receiving signals are small can be judged in terms of existence as a convex portion or a concave portion on the card.
The invention described in Structure (3-20) is a displacement measurement apparatus according to Structure (3-19) wherein the light-irradiating means described in Structure (3-19) irradiates linear light, and the light-receiving means is an array.
By using linear light and by receiving reflected light with array-shaped PD, it is possible to measure multiple locations on a straight line on the card simultaneously.
The invention described in Structure (3-21) is a displacement measurement apparatus wherein intensity of regular reflected light on a flat portion other than a convex portion or a concave portion of the card is greater than intensity of diffused light captured by the converging lens of the invention described in Structure (3-19) or (3-20).
When light is irradiated on a card, reflected light is composed of regular reflected light which is reflected in the direction at an angle for the normal line on the surface of the card, said angle being identical to that for incident light irradiated, and of diffused light.
Since the diffused light from a flat portion and that from a convex portion or a concave portion are in the same intensity in any direction ideally (actually, they are not exactly the same because of a certain extent of directivity), the diffused light from a convex portion or a concave portion enters a light-receiving means through a converging lens. On the other hand, regular reflected light from a convex portion or a concave portion does not pass through the converging lens and does not enter the light-receiving means.
In the invention, intensity of regular reflected light from a flat portion is made to be greater than that of diffused light from a convex portion or a concave portion, which make it possible to discriminate between a flat portion and a convex portion or a flat portion and a concave portion. Incidentally, the greater is the difference of intensity, the easier is the discrimination.